Entanglement rates and haulout abundance trends of Steller (Eumetopias jubatus) and California (Zalophus californianus) sea lions on the north coast of Washington state

Entanglement of Steller sea lions (Eumetopias jubatus) in man-made marine debris on Tyuleniy Island, Sea of Okhotsk

The present report provides data on entanglement of Steller sea lions (SSL) in marine debris on Tyuleniy Island, Sea of Okhotsk. The frequency of entanglement depending on the material, sex, and age of animals was estimated. A total of 133 SSL were recorded as having debris on their bodies, or an average of 22.2 individuals per year. The relative rate of entanglement over the observation years ranged from 1.48 to 1.97% of their total number. The entangled individuals were both males and females of all ages, but young males constituted the largest proportion among them (5.2%). The entangled SSL most frequently (43.2%) had neck collars (the material is not defined) and, less frequently, packaging bands (23.4%), nets (17.7%), and other debris. Most of marine litter found on SSL is associated with commercial fishing activities. On Tyuleniy Island, the rate of SSL entanglement is higher than in the eastern part of the species' range.

Steller Sea Lion (Eumetopias jubatus) at Tuleny Island, Russia in Autumn 2018: Abundance, Composition, and Entanglement

The Steller sea lion (SSL, Eumetopias jubatus) inhabits the North Pacific Ocean off both the North American and Asian coasts. The abundance of the species in Asia declined by more than half in the second part of the 20th century. Decline recurred in the second decade of the 21th century after a short period of restoration. In contrast with the total dynamics of SSL in Asia, the reproductive aggregation on Tuleny I. (Sea of Okhotsk) has been growing almost continuously since the beginning of its formation in the late 1980s. Long-term monitoring of SSL at Tuleny I. always covered only summer reproductive seasons. We surveyed Tuleny I. in October 2018, and counted 1058 non-pup sea lions and 396 pups. The majority of tagged animals encountered at the rookery were of local origin. About one-third of the summer non-pup sea lions' number could remain at the rookery until the middle of October, which coincides with the seasonal appearance of sea lions off the coast of Japan. The sex-age structure was characterized by total absence of adult males and reduced proportion of subadult males and juveniles. It contrasts with autumn behavior of SSLs in the rookery of the northern Sea of Okhotsk. We observed that 0.7% of the inspected sea lions were entangled in marine debris. The proportion of entangled animals is lower in comparison with that of the whole population of Tuleny I. due to reduction in the ratios of males and juveniles, which entangle in foreign objects more often than adult females.